Document number

Maintenance authority

Objectives

The objective is to facilitate sharing and interoperability of geospatial data by providing a flexible and inclusive standard for testing and reporting accuracy of maps and geospatial data.

Scope

The National Standard for Spatial Data Accuracy (NSSDA) implements a well-defined statistic and testing methodology for positional accuracy of maps and geospatial data derived from sources such as aerial photographs, satellite imagery, or maps. Accuracy is reported in ground units. The testing methodology is comparison of data set coordinate values with coordinate values from a higher accuracy source for points that represent features readily visible or recoverable from the ground. While this standard evaluates positional accuracy at points, it applies to geospatial data sets that contain point, vector, or raster spatial objects. Data content standards, such as FGDC Standards for Digital Orthoimagery and Digital Elevation Data, will adapt the NSSDA for particular spatial object representations.

The standard insures flexibility and inclusiveness by omitting accuracy metrics, or threshold values, that data must achieve. However, agencies are encouraged to establish "pass-fail" criteria for their product standards and applications and for contracting purposes. Ultimately, users must identify acceptable accuracies for their applications.

Ground coordinates of points established according to Federal Geodetic Control Subcommittee (FGCS) draft Standards for Geodetic Control Networks and process specifications are used in the National Spatial Reference System (NSRS) control network. NSRS ground control may be used to reference project control surveys to a common georeference system. The accuracy of spatial data derived from control surveys is expressed using the NSSDA. The NSSDA may also be related to FGCS Standards for Geodetic Networks by using NSRS points to test the accuracy of geospatial data. Both the NSSDA and Standards for Geodetic Networks will be integrated into a multipart FGDC Geospatial Positioning Accuracy Standard.

For more information

National Map Accuracy Standard (1947) - Defines accuracy standards for published maps, including horizontal and vertical accuracy, accuracy testing method, accuracy labeling on published maps, labeling when a map is an enlargement of another map, and basic information for map construction as to latitude and longitude boundaries.